Various systems, methods and plants are available for cleaning flue gas. Flue gas contains various components including metals and compounds thereof. It is desirable to limit the concentration of these impurities from the flue gas prior to release of the flue gas into the atmosphere.
Typically, flue gas contains toxic heavy metals, such as lead, cadmium, mercury, barium. Further, flue gas typically contains solid components such as fly ash. These compounds and components are toxic and highly undesirable.
Thus, it is desirable to have these impurities extracted from the flue gas as they are highly toxic to the environment.
In power plants, flue gas resulting from burning of fossil fuel is often used to heat liquids, such as returning district heating water, in order to transfer the heat energy present in the flue gas to the liquid. Then, the heated liquid is often used to provide heat to housing in the surrounding society.
During this heat transfer process, the flue gas condenses, whereby a flue gas condensate is produced. This condensate contains major amounts of the toxic compounds originating from the flue gas. Large plants may produce very large amounts of dirty flue gas condensate. Typically, the production of energy from 1 tonne (1,000 kg) of oil produces approximately 1 tonne of water which is emitted with the flue gas. Production of the same amount of energy from wood (dry wood) requires approximately 2 tonnes of dry wood producing approximately 2 tonnes of water which is emitted with the flue gas. Production of the same amount of energy from e.g. willow requires 4 tonnes of willow (willow has a water content of typically 50%) and produces approximately 4 tonnes of water which is emitted with the flue gas. Thus, flue gas condensates are produced in enormous amounts.
Until the present invention, this condensate has routinely been discharged into the surrounding environment. However, this discharge of condensate presents a substantial risk to the environment and is therefore highly undesirable.
In order to discharge this condensate safely into the environment, it is necessary to remove or substantially reduce the amount of these toxic compounds in the condensate.
However, in order to make such purification feasible for use in purifying flue gas condensate, the process must be simple, effective and inexpensive. Thereby, the condensate may be turned into a resource in a simple and inexpensive way which may be used for a number of purposes including livestock watering, irrigation of crops, wetland habitat production, aquaculture and hydroponics. Thereby, the flue gas condensate can become a valuable resource. However, such potential use requires a sufficient purification of the condensate in order to sustain environmental suitability.
In conventionally used treatment methods, treatment is not sufficiently effective in purifying the flue gas to an environmentally safe level. Especially, the amounts of heavy metals have been unsatisfactory until the present invention in conventionally treated (or untreated) flue gas condensates. Accordingly, there is always a need in the art for more effective purification of flue gas. Further, there is a need in the art for simple and inexpensive methods of reducing the amounts of heavy metals in flue gas condensates.
Further, there is a need in the art for producing flue gas condensate of a quality that makes it a resource for recycling uses.
The concentrated toxic compounds obtainable from the condensate may be used in other industries, e.g. in the cement industry.